1. Field of Invention
The present invention relates to liquid crystal displays, more particularly, to a thin film transistor-liquid crystal display, which prevents the degradation of contrast and improves an aperture ratio thereof, and its method of manufacture.
2. Discussion of Related Art
A liquid crystal display (LCD) is fabricated to provide a state of an image which lessens eye fatigue due to external light reflection and relieves rejection symptoms (an aspect of human engineering). Specifically, LCDs for business or personal uses need a low-reflection technique that functions under a variety of external light conditions.
FIG. 1 shows a layout for a unit pixel of a thin film transistor-liquid crystal display (hereinafter abbreviated TFT-LCD), and FIG. 2 shows a cross-sectional view of the TFT in FIG. 1 along the line II—II, and FIG. 3 shows a cross-sectional view bisecting the TFT-LCD in FIG. 1 along the line III—III.
FIG. 4 shows a cross-sectional view of a portion of a completed TFT-LCD according to the related art. The TFT-LCD, as shown in FIG. 1 and FIG. 4, includes a TFT array plate l, where a TFT and a pixel electrode 30 are arranged; a color filter plate m including a black matrix 29; a color filter (which is denoted by R and G), a common electrode(not shown in the drawing); and liquid crystal 28 filling a space between the plates l and m.
As most LCD manufacturers use a bottom gated TFT—an inverted stagger structure, an LCD according to the related art having a TFT of the inverted stagger structure will be explained in the following description. Referring to FIG. 1, a gate line 10 is disposed horizontally on a transparent substrate 1, which is a TFT array substrate, while a data line 20, which is insulated from and crosses the gate line 10, is arranged perpendicular to the gate line 10. A gate electrode 14 protrudes from the gate line 10 in the direction of the data line 20. As shown in FIG. 2, the gate electrode 14, a gate insulating layer 22 and then an active layer 12 are formed. In the active layer 12, a channel region(not shown in the drawing) is formed over the gate electrode 14, while a source region and a drain region(not shown in the drawing) are defined at both sides of the channel region.
As shown in FIG. 1 and FIG. 2, a source electrode 16, which protrudes from the data line 20, is connected to the source region of the active layer 12, and a drain electrode 18 is connected to the drain region of the active layer 12.
As shown in FIG. 2 and FIG. 3, a passivation layer 24 covers the substrate 1, and includes a contact hole exposing the drain electrode 18. The passivation layer 24 is an insulator having a low dielectric constant. A pixel electrode 30, which covers the contact hole, is connected to the drain electrode 18 via the contact hole. The pixel electrode 30, as shown in FIG. 1 and FIG. 3, may overlap with the data line 20 to increase the aperture ratio.
Referring to FIG. 1 and FIG. 4, reference numeral 32 denotes a window of a black matrix 29, through which light actually passes. In the LCD of the related art, as shown in FIG. 4, a common electrode (not shown) and the respective color filters (denoted by ‘R’ and ‘G’) are formed on the color filter substrate 31, and the black matrix 29 is formed between the color filters R and G. The black matrix 29 is formed of a Cr/CrOx layer (or a metal layer) by sputtering Cr, and prevents light leaking from other regions of the color filters except the window 32 (see FIG. 1). The black matrix 29, which is formed by depositing a metal layer by sputtering, has reduced thickness and low electric resistance. Thus, the cost of fabricating the black matrix 29 is expensive.
While the black matrix 29 reduces degradation such as cross-talk because of its low resistance, the black matrix 29 is affected greatly by external light reflection due to its high reflectivity. Accordingly, Cr/CrOx is widely used for black matrix 29 to reduce such influences because the reflectivity of CrOx is about 3% while that of Cr is 60%.
The aperture ratio of the LCD of the related art is limited because of the LCD's constitution. And, although the LCD of the related art has low reflectivity by using Cr/CrOx as a black matrix, the contrast, which is the ratio of brightness and darkness of an image, is reduced because of the high reflectivity of the data line 20.